Abdominal metastasis of a parosteal osteosarcoma of the femur: An unusual cause of large-bowel obstruction

Background: Parosteal osteosarcoma is a rare, well-differentiated, predominantly fibro-osseous variant of osteosarcoma. It is regarded as a distinct form of osteosarcoma with better prognosis than conventional osteosarcoma. Aim: We report an unusual case of abdominal mass recurrence of parosteal osteosarcoma of the left distal femur treated eight years previously with wide resection, hip disarticulation and chemotherapy, which presented as an acute abdomen: we discuss the clinical outcomes of this rare entity. Case presentation: We present a 54-year-old patient with low-grade parosteal osteosarcoma of the left distal femur. Left total hip disarticulation was indicated after several local relapses of the tumour following extensive resection and chemotherapy. Eight years later, he presented with an acute large bowel obstruction secondary to a compression of the large bowel by an abdominal mass. Abdominal computed tomography showed a large abdominal calcified mass with dilated large bowel loops. During laparotomy, the mass was unresectable. So, the patient underwent emergent colostomy of diversion. Biopsy of the lesion yielded grade III parosteal osteosarcoma material. The patient received adjuvant chemotherapy, but the response was poor: six months later, the patient presented with a peristomal mass and two pulmonary metastases. Conclusion: Abdominal recurrence of parosteal osteosarcoma of the distal femur eight years after definitive surgery is rare. This case emphasises the importance of the long-term follow-up of patients with parosteal osteosarcoma.